Method for making a phosphor layer

Abstract

Making method for a phosphor layer of a small diameter cathode ray tube comprises application of a centrifugal force of above 100G in a direction parallel to the axis of a glass bulb toward its bottom panel to become a face plate, thereby forcedly making sedimentation of phosphor powder onto the inner surface of the bottom panel, and thus, by adoptation of the centrifugal force, a phosphor layer of very fine and dense configuration and uniform thickness is obtainable even using such small medium grain size of phosphor powder of under 4 μm.

What is claimed is: 
     
       1. A method for providing a phosphor layer on the inner surface of a flat bottom panel of a flask-shaped glass bulb, comprising: (a) introducing a phosphor slurry containing phosphor powder of medium grain size of 4 μm or smaller, a small amount of water glass and a small amount of electrolytic substance into a flask-shaped glass bulb having a flat bottom panel with an inner surface and a longitudinal axis generally normal to said flat bottom panel,   (b) thereafter, applying a centrifugal force in a direction parallel to said axis of said glass bulb toward said bottom panel, thereby to forcedly cause said glass bulb to rotate so that its said axis is displaced from vertical substantially towards horizontal and so as to cause sedimentation of said phosphor powder onto said inner surface of said bottom panel,   (c) thereafter, holding said glass bulb stationary for 0.5-15 minutes in a position in which said bottom panel is horizontal and said axis of said glass bulb is vertical,   (d) thereafter, exhausting from said bulb supernatant liquid remaining from said slurry,   (e) thereafter, injecting a washing liquid into said glass bulb, thereby to wash out the glass bulb while retaining said phosphor layer sedimented onto said inner surface and   (f) thereafter, drying said phosphor layer to form a layer of phosphor powder on said inner surface.   
     
     
       2. The method for making a phosphor layer in accordance with claim 1, wherein said water glass is at least one selected from the group consisting of sodium water glass or potassium water glass.   
     
     
       3. The method for making a phosphor layer in accordance with claim 1, wherein said water glass is sodium water glass.   
     
     
       4. The method for making a phosphor layer in accordance with claim 1, wherein said water glass is potassium water glass.   
     
     
       5. The method for making a phosphor layer in accordance with claim 1, wherein said electrolytic substance is a weak electrolytic substance.   
     
     
       6. The method for making a phosphor layer in accordance with claim 1, wherein said electrolytic substance is at least one selected from the group consisting of barium acetate, barium nitrate and potassium sulphate.   
     
     
       7. The method for making a phosphor layer in accordance with claim 1, wherein said electrolytic substance is barium acetate.   
     
     
       8. The method for making a phosphor layer in accordance with claim 1, wherein said centrifugal force is between 100 and 2000 times the magnitude of the force of gravity.   
     
     
       9. The method for making a phosphor layer in accordance with claim 1, wherein said medium grain size is 1-4 μm.   
     
     
       10. The method for making a phosphor layer in accordance with claim 1, wherein said forced sedimentation by centrifugal force is carried out for 3-15 minutes.   
     
     
       11. The method for making a phosphor layer in accordance with claim 1, wherein said glass bulb is for a cathode ray tube having a face panel of about 3 inches of diagonal length.